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| United States Patent |
5,639,958
|
|
Lange
|
June 17, 1997
|
Device and a method for localizing leakages in conduit networks
Abstract
Device and method for locating leaks in pipelines, overhearing even weak
sounds, from leaking fluid especially in pipelines made of material with
limited sound conductivity such as plastic. The device includes a first
thin diaphragm with one side in contact with the fluid, whereby vibrations
are transferred from the fluid to a second diaphragm joined to the
opposite side of the first diaphragm. The second diaphragm is made of a
preferably sound-sensitive piezoelectrical plastic foil, the diaphragms
being able to co-vibrate with frequencies from one to a few thousand
Hertz. The first diaphragm protects against the inner pressure in the
liquid line and moderates any sympathetic vibration. The low-frequency
A.C. that is generated by the vibration in the second diaphragm is
amplified and transposed to a range of frequencies that is audible for the
human ear.
| Inventors:
|
Lange; Gosta (Goteborg, SE)
|
| Assignee:
|
Ingenjorsfirma Ultrac AB (SE)
|
| Appl. No.:
|
530207 |
| Filed:
|
January 25, 1996 |
| PCT Filed:
|
March 29, 1994
|
| PCT NO:
|
PCT/SE94/00283
|
| 371 Date:
|
January 25, 1996
|
| 102(e) Date:
|
January 25, 1996
|
| PCT PUB.NO.:
|
WO94/23242 |
| PCT PUB. Date:
|
October 13, 1994 |
Foreign Application Priority Data
| Current U.S. Class: |
73/40.5A; 73/40; 73/592 |
| Intern'l Class: |
G01M 003/24; G01N 029/04; F22B 037/42 |
| Field of Search: |
73/40.5 A,592,40
|
References Cited
U.S. Patent Documents
| 2008934 | Jul., 1935 | Smith | 137/77.
|
| 3596510 | Aug., 1971 | Siegel et al. | 73/149.
|
| 4043180 | Aug., 1977 | Morris et al. | 73/40.
|
| 4309576 | Jan., 1982 | Corrigan | 179/110.
|
| 4435974 | Mar., 1984 | Fuchs et al. | 73/40.
|
| 4498333 | Feb., 1985 | Parthasarathy | 73/40.
|
| 4543817 | Oct., 1985 | Sugiyama | 73/40.
|
| 4583406 | Apr., 1986 | Dimeff | 73/592.
|
| 4779246 | Oct., 1988 | Dietzsch et al. | 367/157.
|
| 4785659 | Nov., 1988 | Rose et al. | 73/40.
|
| 4810913 | Mar., 1989 | Beauducel et al. | 310/337.
|
| 4960079 | Oct., 1990 | Marziale et al. | 122/504.
|
| 5101774 | Apr., 1992 | Marziale et al. | 122/504.
|
| 5117676 | Jun., 1992 | Chang | 73/40.
|
| 5361636 | Nov., 1994 | Farstad et al. | 73/592.
|
Other References
Derwent's abstract, No. 89-148814/20, week 8920, Abstract of SU, 1413354
(Introscopy Res Inst), Jul. 30, 1988.
|
Primary Examiner: Williams; Hezron E.
Assistant Examiner: Wiggins; J. David
Attorney, Agent or Firm: Finnegan, Henderson, Farabow, Garrett & Dunner, L.L.P.
Claims
I claim:
1. A device for localizing leakages in a conduit network by listening for
leakage sounds emanating from a leaking liquid in conduits that are
constructed from plastics and other materials having low acoustic
conductivity, comprising a first, thin diaphragm having one side oriented
to lie in contact with the liquid and a second side oriented not to lie in
contact with the liquid, a second sound-responsive diaphragm that is
attached to and overlies the second side of the first diaphragm with a
common interface therebetween, wherein said first diaphragm is designed to
transmit oscillations from the liquid to the second diaphragm by the
coupling of forced mechanical oscillations across the interface, said
second diaphragm being made of a piezoelectric material in a
sound-responsive, piezoelectric plastic sheet, wherein said first and said
second diaphragms are able to oscillate together at frequencies of from
zero to seven thousand Hertz, and wherein said first diaphragm is designed
to withstand the internal pressure in the liquid conduit and to protect
the second sound-responsive diaphragm against direct contact with said
liquid, and also to attenuate any resonance oscillations of the conduit
network comprising said liquid in the conduits, and an amplifier for
amplifying the low-frequency electric alternating current signals
generated by the oscillations in the second sound-responsive diaphragm and
means for transposing the amplified signals to a frequency range which can
be readily heard by the human ear.
2. A device according to claim 1, wherein the first diaphragm has a
thickness of 0.05-0.6 mm.
3. A device according to claim 2, wherein the first diaphragm is made of
metal.
4. A device according to claim 1, wherein the first diaphragm is made of
stainless steel.
5. A device according to claim 1, wherein said device is constructed so
that the diaphragms are positioned generally parallel with the
longitudinal direction of the conduit and therewith minimize the influence
of longitudinal oscillations in the conduit material on the surface of the
diaphragm.
6. A device according to claim 1, wherein electrical conductors are
connected from the sound-responsive second diaphragm to said transposing
means, said transposing means including a frequency converter which is
connected to a pair of earphones via said amplifier connected to the
output of the frequency converter.
7. A method for localizing leakages in a conduit network by means of a
device according to any of claims 1-5 or 9, including transposing the
sound from the low-frequency sound occurring in the conduit network to
sound that can be clearly heard by the human ear by a digital sampling
technique with the aid of FFT (Fast Fourier Transform) and an inverse
transform.
8. A method according to claim 7, further including creating a frequency
spectrum mathematically with the aid of FFT, and multiplying this spectrum
frequency-by-frequency so as to obtain a spectrum of elevated frequencies,
and creating a new acoustic signal of higher frequency with the aid of an
inverse transform.
9. A device according to claim 1 wherein the transposing means first
receives the low-frequency electric alternating current signals generated
by the oscillations in the second sound-responsive diaphragm and
transposes these signals to a frequency range which can be readily heard
by the human ear, and wherein the amplifier amplifies these transposed
signals.
Description
TECHNICAL FIELD
The present invention relates to a device and to a method for localizing
leakages in conduit networks, by listening for sound, even slight sound,
generated by leaking liquid, particularly in pipe systems that are
comprised of materials which have only low sound conductivity, such as
plastic materials and the like.
DESCRIPTION OF THE BACKGROUND ART
Roughly 25% of the amount of liquid distributed in extensive conduit
networks, for instance networks which convey water or oil under pressure,
is lost because of leakage in the system. This is a serious problem with
regard to economy and also with regard to the environment.
One method of minimizing these drawbacks is to have at one's disposal an
effective and simple auxiliary device by means of which the distribution
system can be checked with the intention of discovering a possible leakage
as early as possible.
Personnel engaged in finding leaks are accustomed to relying on their own
hearing to ascertain the presence of a leak, by listening directly. It is
difficult, however, for the human ear to discern sound that has been
propagated in a leaking plastic pipe.
It is also difficult to discern the sound of a leak against background
noise, for instance against pronounced traffic noise.
Many different technical solutions relating to listening devices for
localizing leakages in different types of pipe systems are known within
this technical field. The sounds generated by a substance leaking from a
pipe or conduit can be listened for directly, or is signal processed in
different ways. Various listening methods have been developed, such as the
arrangement of electronic amplifiers which have enabled even relatively
weak sound to be discerned. These amplifiers must be used together with
acoustic sensors which convert the pressure waves into electric signals.
In this regard, there have been used microphones which are pressed
directly against pipes or fittings in the same way as the ear of the
listener is pressed when listening directly. However, it has been found
that the best method of discovering leakages, even small leakages, is to
listen directly against the liquid or substance concerned. This is best
effected with the aid of a hydrophone, which is coupled to the liquid
either through a separate hole drilled in the conduits, or by passing the
hydrophone to existing fire cocks, fire hydrants or the like, which are
opened so that the water is able to rise to the level of the sensing
surface of the hydrophone.
These devices cannot normally be used, however, in conduit networks in
which the conduits or pipes are made of a plastic material, for instance,
since essentially only low acoustic frequencies of the leakage sound are
able to propagate over longer distances in the pipes. These sounds cannot
be heard by the human ear, not even with the aid of an amplifier and
earphones. It is therefore necessary to use electronic measuring apparatus
in cases such as these. This means that the person who is specially
trained to find leakages and who is accustomed to listen for sound in
cast-iron pipes is unable to apply his expertise in deciding whether or
not there is a leakage in the modern plastic pipes. This is a very serious
drawback, since the human hearing is paramount with regard to
distinguishing between different sounds that occur in pipes, i.e. between
leakage sounds or traffic sounds.
The acoustic converters used in hydrophones are normally comprised of
piezoelectric crystals having a high resonance frequency, e.g. a frequency
of 100 kHz. This crystal can be combined with a mechanical element, such
as a diaphragm, having a lower resonance frequency.
Examples of such known devices are found in U.S. Pat. Nos. 2,008,934,
4,435,974, 4,236,235, 4,779,246 and 4,810,913.
The device taught by U.S. Pat. No. 4,779,246 includes a diaphragm which has
been tensioned in a way to provide the lowest resonance frequency.
BRIEF DISCLOSURE OF THE INVENTIVE CONCEPT
The object of the present invention is to eliminate the aforesaid
disadvantages and drawbacks of devices for listening for leakage sounds in
extensive pipe or conduit network systems.
Conventional devices that include an accelerometer which is pressed against
a pipe wall or a valve spindle provide a relatively poor
signal/disturbance ratio. There is also the risk of poor contact with the
pipe wall.
When a hydrophone is used, the best listening range will depend on direct
contact between the listening element and the medium.
The hydrophones that are available commercially are normally constructed
for general measuring purposes and therefore have a very wide frequency
range and are not optimally or directly suited for leakage finding.
These hydrophones are usually mounted in conduit networks so as to be
sensitive or responsive to oscillations that are propagated in the pipe
wall, meaning that traffic generated vibrations, for instance, will be
fully detected.
One known method of increasing the frequency of an acoustic signal is to
record the sound on a tape recorder which operates at a low speed and then
play back the sound at a higher speed.
Another method is to record signals digitally with the aid of so-called
sampling.
Both of these methods give "time slots" in playback, since they require the
recordings to be played back at a faster speed than they were made. The
sound is normally repeated and fills the slots, although at the cost of a
poorer sound quality.
To achieve the objects and in accordance with the purpose of the invention,
as embodied and broadly described herein, the device for localizing
leakages in a conduit network of this invention comprises a first, thin
diaphragm having one side oriented to lie in contact with a liquid and a
second side oriented not to lie in contact with the liquid, a second
sound-responsive diaphragm that is attached to and overlies the second
side of the first diaphragm with a common interface therebetween, wherein
the first diaphragm is designed to transmit oscillations from the liquid
to the second diaphragm by the coupling of forced mechanical oscillations
across the interface, the second diaphragm being made of a piezoelectric
material in a sound-responsive, piezoelectric plastic sheet, wherein the
first and the second diaphragms are able to oscillate together at
frequencies of from zero to seven thousand Hertz, and wherein the first
diaphragm is designed to withstand the internal pressure in the liquid
conduit and to protect the second sound-responsive diaphragm against
direct contact with the liquid, and also to attenuate any resonance
oscillations of the conduit network comprising the liquid in the conduits,
and an amplifier for amplifying the low-frequency electric alternating
current signals generated by the oscillations in the second
sound-responsive diaphragm and means for transposing the amplified signals
to a frequency range which can be readily heard by the human ear. The
diaphragm can be oriented in said device essentially parallel with the
longitudinal direction of the conduit, so as to minimize the influence of
oscillations in the conduit material on the surface of the diaphragm.
This construction renders the diaphragm insensitive to oscillations in the
longitudinal direction of the conduit, i.e. directions which are parallel
with the diaphragm surface, while enabling medium-carried sound that
impinges transversely to the diaphragm surface to be discovered.
There is also provided in accordance with the inventive concept a device
which is highly responsive to leakage sound, i.e. will allow dynamic
pressure oscillations to pass through but isolates static pressure,
wherein the device is reliable in operation, for instance the possible
presence of an air cushion between medium and diaphragm will not cause any
appreciable attenuation of the acoustic signals, and a device which has
low response to ground-carried disturbances and which can be applied
easily to different parts of the conduit network, and in which device the
recorded sound signal is converted to a higher frequency that is audible
to the human ear, by FFT-conversion, multiplication and inverse
FFT-processing.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail with reference to the
accompanying drawings, in which
FIG. 1 is a sectioned view of the invention;
FIG. 2 illustrates frequency response curves for: B a piezoelectric crystal
connected to a diaphragm with resonance; A a conventional piezoelectric
crystal; and C shows the frequency response curve for the present
invention;
FIG. 3 illustrates frequency response curves representative of the leakage
sounds occurring in conduits, E in plastic conduits and D in iron
conduits;
FIG. 4 is a diagram illustrating a small section taken from the curve form
of the original acoustic signal;
FIG. 5 illustrates sections that have been taken from the curve in FIG. 4
and recorded at elevated speeds;
FIG. 6 is a diagram illustrating an acoustic signal;
FIG. 7 illustrates the frequency spectrum of the acoustic signal shown in
FIG. 6, according to FFT; and
FIG. 8 illustrates the newly converted acoustic signal of higher frequency.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
As will be apparent from FIG. 1, the inventive device includes a first
circular diaphragm 1 which is made of thin stainless steel, for instance,
and has a thickness of 0.05-0.06 mm. The diaphragm is attached to a rigid
holder 2, for instance welded or soldered thereto. The diaphragm includes
a surface 3 which is intended to lie in contact with the water conducted
by the conduit system and is able to withstand the pressure of 6-10
kg/cm.sup.2 prevailing in the conduits. The diaphragm also has an inner
surface 4 on which a second diaphragm 5 is firmly mounted. This second
diaphragm is comprised of a piezoelectric plastic sheet which is flexible
and accompanies the movements of the first diaphragm, therewith generating
electric signals.
These electric signals are passed through electric conductors 6 to a device
7 which analyzes the low frequency sound recorded and converts the
frequency, whereafter the electric signals are sent to an amplifier 8 to
which there is connected a pair of earphones 9. The holder 2 is
constructed to enable it to be applied to a fire cock or fire hydrant 10,
for instance, and is provided with a packing 3' for sealing the holder on
the hydrant. The analyzing apparatus and the frequency converter 7 contain
electronic circuits for transposing sound of low frequency to sound of
higher frequency, so that the sound can be discerned by the human ear. In
this regard, the acoustic signals are sampled in accordance with sampling
techniques and the acoustic signals are then compressed by excluding or
shortening the interval between the sampling processes. As a result, the
bandwidth is also transposed in addition to the frequencies, which means
that the sound will have the same character as that normally emanating
from iron conduits.
FIG. 2 illustrates frequency response curves for: B a piezoelectric crystal
coupled to a diaphragm that has resonance; A a conventional piezoelectric
crystal; and C illustrates the frequency curve obtained with the present
invention. It is evident from the diagram that neither the curve A nor the
curve B cover low frequencies, whereas the curve C has uniform sensitivity
or responsiveness from zero frequency and upwards.
FIG. 3 illustrates the frequency response curves representative of the
leakage sounds that occur in conduits, E in plastic conduits and D in iron
conduits.
A comparison between the curves shown in FIG. 3 shows that conventional
diaphragm constructions can be used when listening for sound in iron
conduits, although the response to sound is very poor with regard to
plastic conduits, whereas a device constructed in accordance with the
inventive principles can be used efficiently in both iron and plastic
conduits.
FIGS. 4 end 5 illustrate digital recording of a signal with the aid of
sampling. FIG. 4 shows small sections taken from the curve form of the
original acoustic signal, and FIG. 5 shows the sections taken from said
curve form and played back at higher speeds. FIG. 6 illustrates a curve
representative of an incoming low-frequency acoustic signal, which for the
sake of clarity has been shown as sinusoidal but which in practice can
have any form.
FIG. 7 illustrates a typical sound spectrum for a curve according to FIG.
6, and shows how the same spectrum can be moved to a higher frequency
range by multiplication.
FIG. 8 illustrates the newly converted acoustic signal of the higher
frequency, which corresponds to the spectrum in FIG. 7 moved to a higher
frequency.
The device components can be assembled and joined by welding, gluing or
corresponding processes.
MODIFICATIONS OF THE INVENTION
It will be understood that the invention is not restricted to the described
and illustrated embodiments thereof and that modifications can be made
within the following claims. For instance, the frequency can be transposed
by recording the signals digitally, with the aid of sampling.
The inventive device can also be used as an acoustic transmitter when an
electric voltage is applied to the piezoelectric diaphragm. This diaphragm
will then function as a sound transmitter and can be used in searching for
buried plastic conduits whose positions are not completely known.
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